Vacuum device process



United States Patent 3,239,300 VACUUM DEVICE PROCESS Adolph J. Fiedor, Palo Alto, and Robert G. Rockwell, Menlo Park, Califl, assignors to Varian Associates, Palo Alto, Calif., a corporation of California No Drawing. Filed Apr. 1, 1963, Ser. No. 269,804 7 Claims. (Cl. 316-24) This invention relates in general to electron discharge devices and, more particularly, to a novel method for processing gold-plated electron tubes.

Gold plating has been utilized on metal bodies of electron beam tubes such as klystrons, magnetrons, etc, in the past for a number of reasons, examples of which are the good thermal conductivity and corrosion free properties provided by such a coating. Such coatings allow very good thermal contact of the tubes with external heat sinks, cooling fluids such as oil, fluorocarbons, etc. and thus allow maintenance of good temperature stability. In addition, the coating protects against oxidation, an effect which hinders good electrical contact with associated apparatus such as waveguide flanges in output transmission lines and the like. Also, in oil baths and other types of liquid or gaseous environments, gold plating is more chemically inert or resistant than paint, another common coating substance. In addition, gold plating, because of its unsurpassed malleability, resists marring and scratching better than other coatings such as paint.

Although gold plating is advantageous in the above respects, applicants have discovered that certain problems arise when gold plating is utilized on such vacuum devices. In carrying out the gold plating by conventional techniques, the klystron tube is first assembled and then evacuated and processed in the normal manner after which the tube is gold plated electrodeposition. The klystron is immersed in the plating bath of gold cyanide water solution and is electrically connected as the cathode in the electrolytic bath. In order to deposit a sufiiciently thick gold plate on the tube, a suitable high potential, over a prolonged time, such as 30 minutes, must be applied between the klystron and the anode in the bath to produce the desired gold plate throwing power. Applicants have discovered that such thickly plated klystrons have, after complete assembly and gold plating, become gassy during subsequent operation of the klystron. Applicants have determined that this gaseous condition is brought about due to hydrolysis which occurs in the plating bath during the electroplating process. The hydrolysis releases nascent hydrogen, also known as atomic hydrogen, and represented by the symbol H+. Nascent hydrogen is the smallest atom and thereby diffuses into the intermolecular spaces of the metals constituting the electron device which is being gold-plated. Subsequent to the removal of the tube from the gold-plating solution, the nascent hydrogen dilfuses throughout the metals. At the interior and exterior surfaces of the tube, the nascent or atomic hydrogen recombines as diatomic hydrogen H and is released. At the exterior surfaces there is simply release of the diatomic hydrogen into the atmosphere; whereas at the interior surfaces of the tube, the diatomic hydrogen is released into the vacuum space of the tube and results in a gassy tube. This can be detected in a reflex klystron tube, for example, by excessive current drain from the cathode supply and by a gas current measurement using the reflector supply. The release of diatomic hydrogen occurs with time and/ or as a result of heating of the tube during subsequent operation.

In the method of this present invention, the applicants eliminate the problems encountered by the gas absorbed by diffusion during the gold plating by the additional step of evacuating the tube after it has been gold plated 3,239,300 Patented Mar. 8, 1966 ice to thereby pump the diffused gases out from the vacuum tube body and associated structural elements.

It is, therefore, the object of the present invention to provide a novel method for processing gold-plated vacuum tubes to render them substantially gas free after plating.

One feature of the present invention is the inclusion, in the processing of gold-plated evacuated devices, such as an electron discharge device, of the step of evacuating the devices by vacuum pumping after the electrodeposition gold-plating to remove gas produced therein from the plating bath.

The steps in one suitable method for processing a vacuum device, for example, a reflex klystron, in accordance with the present invention are as follows:

The klystron is completely assembled, including all of the vacuum seals, and brazed to form the vacuum tight envelope, the tube being connected by means of a tubulation to two suitable vacuum pumps, for example, a 5 liter :per second and a 1 liter per second electronic sputter ion pump, both of which are available commercially. This assembly is made completely vacuum tight and ready for subsequent processing.

The klystron is placed in a conentional tube bakeout oven with the two pumps outside the oven. The oven temperature is brought up to suitable bakeout value, for example 500 C., while a temperature of the order of 200 C. is applied to the small 1 liter pump for initial outgassing of this pump. The 5 liter pump is operated to evacuate the reflex tube and the 1 liter pump to the desired high vacuum, such as 10- Torr.

After bakeout for the time necessary to outgas, about four hours, the tube is returned to room temperature and the cathode therein is then activated, i.e. the necessary electrical potentials are applied to activate the coating on the cathode face and produce the electron beam and the tube is brought up to maximum operating potentials. During this period the 5 liter pump is continuously operating to pump out any gases that may be released during this activation period. The activation continues until the tube is completely outgassed, after which the tube is deenergized and the 5 liter pump is pinched oif, thus leaving the tube and the 1 liter pump in a highly evacuated assembly.

If desired or necessary, additional adjustments may be made to the tube at this point, for example, alignment of the cathode and reflector assemblies with the resonator cavity or cavities by known techniques.

The klystron tube is then placed in the well known gold plating bath, for example, a potassium gold cyanide solution, and is connected as the cathode in the bath at a suitable potential for the particular plating tanks employed. The tube is gold plated for the time necessary to produce the desired thickness of plating on the tube, for example, 0.0003", which in applicants plating tank required about 30 minutes of plating time. During this time, gas from the plating bath, in particular, nascent hydrogen, diffuses into the klystron body as explained above.

It is this gas which, in prior gold-plated tubes, diffused through the body and, eventually, resulted in high gas pressures within the tube. The end result was excessive beam currents which could melt or damage cavity resonator grids and change the optics of the tube sufficiently to result in poor tube operation.

After gold-plating, the tube is removed from the bath and is again placed in a bakeout oven which is heated to about 370 C. During this bakeout period, the 1 liter sputter ion pump is energized and serves to pump the gas, which has resulted from the plating, from within the tube.

In addition to, or in some applications in lieu of the second oven bakeout just cited at 370 (3., suitable potentials are next applied so as to produce the electron 3 beam and thus heat up the interior portions of the tube to a temperature substantially higher than above so as to liberate the gases diffused into those parts of the klystron which normally operate above 370 C. During this period the 1 liter sputter ion pump is energized and serves to pump the gas evolved.

The tube is then ready for any desired finishing step such as connection and potting of the heater, cathode and reflector leads. During and after this step, the 1 liter pump is energized to maintain the pressure within the klystron at the desired low value, after which the pump is pinched-off from the tube.

It should be understood that the 1 and 5 liter pumps may be connected to the tube by any form of suitable valving means. For example, the 5 liter pump may be an integral part of a pumping station which also includes the bakeout oven. Also, the pumping after gold-plating may be accomplished by a pump, such as the 5 liter pump, associated with the bakeout oven used after plating and in this case the 1 liter pump may be omitted.

An alternate procedure for carrying out the process of the present invention is as follows. The tube is completely assembled so as to be vacuum tight and attached as by a tubulation tube to a l liter/sec. sputter ion pump. The tube is then placed in the gold-plating bath and the desired thick plating of gold applied in known manner by the electrodeposition technique.

The tube is then taken to the pumping station including the bakeout oven and the 5 liter/sec. pump to which the tube is coupled. The tube is then baked out at a temperature of, for example, 500 C. with both the l and liter/sec. pumps operating to pump out the tube.

After bakeout and when the desired high vacuum is obtained in the tube, the tube cathode is activated to produce the desired electron beam flow in the tube during which time both the 5 liter and 1 liter pumps are operating to further outgas the tube during activation. When the desired vacuum has been reached, the tube is valved or pinched-off from the 5 liter/sec. pump.

At this time, aligning of the tube may take place, if desired or necessary, to obtain maximum power output; during this alignment the 1 liter/ sec. pump may be operated for clean-up purposes.

The tube is then returned to the gold-plating bath for the application of a finish coating of gold. This is done to obtain a bright gold finish coat in lieu of the rose gold finish which occurs on the original coating due to the bakeout at 500 C. The tube is then returned to the bakeout oven to be again heated, but to a lower temperature, for example 370 C. during which time the 1 liter pump is operated to remove any gases that may have been formed in the tube during the finish plating bath. To protect the finish coat against discoloration, if desired, the tube may be coated with a washable protective coating, such as Markal protective coating C-R- obtainable from The Markal Company of Chicago, Illinois, which may be washed off after removal of the tube from the bakeout oven.

After the tube has reached the suitable vacuum, it is removed from the oven and further operative steps may be performed on this tube, including, for example, attachment of leads connecting to the gun and reflector, the molding of silastic on the cathode and reflector ends of the tube, and the like.

As a last step, the tube is again operated by application of suitable voltages and the electron beam used to raise the body temperature to about 250 C. During this period, the 1 liter pump is operated as a last pumpdown stage, after which the 1 liter pump is pinched-off from the tube which is now ready for normal operation.

It is noted that in the above processing techniques, the important feature is the evacuation by suitable vacuum pumping means of the device after it has been goldplated by electrodeposition to insure that gases formed within the tube due to and as a result of hydrolysis in the plating bath are removed. It can thus be seen that many variations may be made in the overall processing of such vacuum devices and that the above examples of reflex klystron tube processing are merely illustrative of the use to which the present invention may be applied.

What is claimed is:

1. The method of processing gold-plated devices designed to be operated in the evacuated condition comprising the steps of assembling the device in a vacuum-tight condition, heating said device in a bakeout oven to cause gas to be liberated within the device, evacuating said device with a vacuum pump while heating to thereby pump out the liberated gases from the device, subsequently placing said discharge device in a gold plating bath solution and depositing a coating of gold on said device by electrodeposition, again evacuating said device with a vacuum pump to remove gases therefrom including gases diffused into the device from the plating bath, and sealing ofl said device from said vacuum pump after said device has been evacuated to the desired low pressure.

2. The method as claimed in claim 1 including the step of heating the device during the second evacuation stage to aid in the outgassing of the device.

3. The method of processing an electron discharge device comprising the steps of assembling the device including the electron beam source in a vacuum-tight condition, heating said device in a bakeout oven to cause gas to be liberated within the device, evacuating said device with a vacuum pump while heating to thereby pump out the liberated gases from the device, subsequently placing said discharge device in a gold plating bath solution and depositing a coating of gold on said device by electrodeposition, again evacuating said device with a vacuum pump to remove gases therefrom including gases diffused into the device from the plating bath, and sealing off said device from said vacuum pump after said device has been evacuated to the desired low pressure.

4. The method of processing an electron discharge device as claimed in claim 3 including the step of activating the electron beam source in said device at a time during at least one of the periods of evacuation of said device to heat up said device during the evacuation period to aid in outgassing the device.

5. The method of processing an electron discharge device comprising the steps of assembling the device including the electron beam source in a vacuum-tight condition, placing said discharge device in a gold plating bath solution and depositing a coating of gold on said device by electrodeposition, coupling said device to a vacuum pump for evacuating the device by removing gases therefrom including gases diffused into the device from the plating bath, heating the device in an oven to several hundred degrees centigrade to aid in liberating gases within the device, again placing the device in a gold plating bath to deposit a finish coating of gold on said device by electrodeposition, again heating the device to liberate gases from within the device including gases diffused into the device from the bath, evacuating the device with a vacuum pump during the second period, and then sealing off said tube from the vacuum pump.

6. The method as claimed in claim 5 including the step of activating the beam source in the device during at least one of said evacuation times.

7. The method as claimed in claim 6 including the step of activating the beam source in the device during both said periods of evacuation.

References Cited by the Examiner UNITED STATES PATENTS 1,872,336 8/1932 Ulrey 316-24X 2,748,067 5/1956 Pease et al. 204-37 FRANK E. BAILEY, Primary Examiner. 

1. THE METHOD OF PROCESSING GOLD-PLATED DEVICES DESIGNED TO BE OPERATED IN THE EVACUATED CONDITION COMPRISING THE STEPS OF ASSEMBLING THE DEVICE IN A VACUUM-TIGHT CONDITION, HEATING SAID DEVICE IN A BAKEOUT OVEN TO CAUSE GAS TO BE LIBERATED WITHIN THE DEVICE, EVACUATING SAID DEVICE WITH A VACUUM PUMP WHILE HEATING TO THEREBY PUMP OUT THE LIBERATED GASES FROM THE DEVICE, SUBSEQUENTLY PLACING SAID DISCHARGE DEVICE IN A GOLD PLATING BATH SOLUTION AND DEPOSITING A COATING OF GOLD ON THE SAID DEVICE BY ELECTRODEPOSITION, AGAIN EVACUATING SAID DEVICE WITH A VACUUM PUMP TO REMOVE GASES THEREFROM INCLUDING GASES DIFFUSED INTO THE DEVICE FROM THE PLATING BATH, AND SEALING OFF SAID DEVICE FROM SAID VACUUM PUMP AFTER SAID DEVICE HAS BEEN EVACUATED TO THE DESIRED LOW PRESSURE. 